Macrocyclic compounds are used to complex metal counterions and thereby change the interfacial properties of anionic micelles and mica. Macrocyclic cryptate ligands (C221 or C222) or the crown ether (18-crown-6) were added to surfactant solutions of lithium, sodium, potassium, calcium, or barium dodecyl sulfate. This resulted in lower critical micelle concentrations, decreased aggregation numbers, which are insensitive to added salt, and larger interfacial areas per molecule. Surface forces measurements show that the mica counterion complexation effects are less dramatic. Addition of C222 to potassium or barium salt solutions results in significant increase in the separation of the mica surfaces at "contact", but almost no change in the surface potential. These results provide a basis for comparing counterion effects for colloidal interfaces with fixed and labile surface charges.

The colloidal forces between dihexadecyldimethylammonium bilayers immersed in formamide were measured by using the surface forces apparatus. The forces were determined as a function of added sodivm acetate and potassium bromide and found to be almost identical with those observed in water. These observations establish that the unusual counterion effects observed for amphiphiles in aqueous solution are not a consequence of the unique structural properties of water.The self-assembly of surfactants is not unique to water but is a general feature of polar hydrogen-bonding solvents including hydrazine,1-2 ethylammonium nitrate,* f~r m a m i d e ,~ and ethylene glyc01.~ The characterization of surfactant aggregation in these nonaqueous solvents has focused mainly on the role of solvophobicity in driving the aggregation processes. The role of counterion effects which are so prominent in water has been virtually ignored in other solvents. In this note we present surface forces measurements which compare counterion effects in formamide and water.In aqueous solution, counterions play an important role in determining the type of amphiphilic microstructure formed. For example, at room temperature dialkyldimethylammonium halides form bilayers while the corresponding carboxylate and hydroxides form spontaneous vesicles in dilute solution and spherical micelles in more concentrated s~l u t i o n .~ Similar types of transformations are observed with double-chained anionic surfactants such as SHBS (sodium 8-phenyl-1-hexadecane-p-sulfonate) when the counterion interaction is modulated by the addition of cryptate complexing agents. These observations suggest that the aggregation patterns of double-chained surfactants is more subtle than previously thought.For the cationic surfactants the following story has emerged. With alkyltrimethylammonium acetate and hydroxide micelles, counterion binding is greatly reduced compared to the halide^.^ This in turn increases head group repulsion, increases curvature at the aggregate-water interface, and results in micelles with lower aggregation numbers. These observations can be rationalized in terms of theory provided that the average counterion distance for the carboxylates is displaced from the surfactant head groups by 4 A.S This implies a higher degree of hydration by water for the carboxylates compared to the halides. Extension of these ideas to double-chained surfactants suggests that substitution of carboxylates for the halides would result in similar curvature effects and thereby transform bilayers to vesicles.Further insight into the difference between the halides and carboxylates in aqueous solution comes from surface forces measurement^.^ In these experiments, dihexadecyldimethylammonium bilayers are formed on the two mica surfaces and the force vs. distance curves measured as a function of added sodium acetate and potassium bromide. With the acetates, a repulsive ( 1 ) Ramadan, M.; Evans, D. F.; Lumry, R. J. Phys. Chem. 1983,87,4538. (2) Evans, D. F.; Yamauchi, A.; Roman, R.; Casass...

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Analytical tracer techniques for studying the role of sulfur dioxide in air pollution problems were developed. An apparatus was built which made it possible to measure directly microgram quantities of sulfur dioxide tagged with S36. The tagged sulfur dioxide

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